The present invention relates to a new and improved construction of apparatus or installation for continuous casting metals, typically steel, with high throughput.
During the continuous casting of steel, the strand departing from the essentially vertically arranged continuous casting mold, and which strand possesses an outer shell or skin and a long liquid core, normally is guided and simultaneously cooled at a roller apron along a desired path of travel into a horizontal path of travel. By means of a withdrawal and straightening apparatus the strand is conveyed and straightened. The ferrostatic pressure acting upon the shell of the strand is taken-up by the rollers.
In the case of continuous casting installations or plants operating at high throughput capacity, in other words, with continuous casting speeds exceeding 1 meter per minute for casting large slab cross-sections, there are required rollers of large diameter for supporting the forces acting upon the strand shell owing to the ferrostatic pressure. Hence, at the region following the continuous casting mold, that is to say, at the region of the strand which still has a thin outer shell or skin, it is not possible to prevent bulging thereof because of the large distances between the rolls or rollers. Such bulging produces the well-known metallurgical defects, such as fissures and the like, which also can lead to metal breakout. Furthermore, a large withdrawal force is necessary since such bulging portions of the strand must be again pushed back by the rollers to the adjusted rated value.
To avoid such bulging between the rollers at higher casting speeds, it is known in this particular art to arrange cooling plates and/or cooling grids at the region of the still thin strand shell. In the case of cooling plates, the ferrostatic pressure acting upon the strand shell is taken up in the lengthwise and transverse directions by the plate surfaces and cooling water is introduced between the strand- and plate surfaces. In the case of cooling grids the support action occurs only partially lengthwise and transverse to the strand, the unsupported surfaces being impinged with cooling water. Such equipment permits casting at high casting speeds without bulging of the thin shell or skin. However, what is disadvantageous with such equipment is the presence of great frictional forces, so that the length of such support zones is limited.
According to an unpublished proposal, the drawbacks associated with the bulging at the strand having a large cross-section at a continuous casting installation operating at high throughput, for instance with casting speeds in the order of 2 meters per minute and more, are intended to be avoided and the withdrawal force reduced, in that the surface of the strand between the mold and the location of complete solidification of the strand is subjected to a gaseous medium which is under pressure. For this purpose there is required a pressure compartment or chamber arranged about the strand and as the gaseous medium there is employed water vapor produced by the water sprayed onto the surface of the strand. Since the ferrostatic pressure at the curved portion changes; the pressure compartment is subdivided at this region or portion, so that it is possible to approximately adjust the counterpressure corresponding to the momentary ferrostatic pressure.
Since for practical reasons such compartment subdivision, however, cannot be carried out to be too small, there are present small pressure differences between the ferrostatic pressure and the counterpressure. Likewise there cannot be avoided defect locations at the frozen shell, for instance slag inclusions and so forth, so that the danger of metal breakout at the immediate regions following the mold is not completely eliminated. Steel flowing out to the pressure compartment containing the vapor and water, however, leads to the inlcusion of such media, so that there cannot be prevented explosions and thus damage to the pressure compartment.